The present invention generally relates to transonic wings for flight vehicles and more particularly to a wing trailing edge yielding an improved ML/D ratio.
The aerodynamic drag of modern transonic wings consists of three components: lift-induced drag, profile drag and compressibility drag. Profile drag includes skin friction related drag and base drag due to trailing-edge bluntness. At relatively slower speeds (Mach numbers below the design condition), the wing drag consists of the lift-induced drag and profile drag. As the speed is increased, shock waves appear on the wing surface. These shock waves cause increased drag and are the major portion of the drag that was referred to above as compressibility drag. Compressibility drag increases dramatically with increasing speed and strongly limits the efficiency of a wing in terms of its lift-to-drag ratio. For example, modern air transport wing designs are developed to delay the onset of this drag rise until a point that is above a cruise design speed condition. The aerodynamics engineer utilizes both wing sweep and airfoil section characteristics as the primary variables in achieving a design that sufficiently delays the onset of compressibility drag while also attaining high lift and low drag.
Another consideration for the aerodynamics engineer related to the design of an efficient aircraft is trim drag. Trim drag is the drag associated with balancing the lifting forces with the center of gravity of the flight vehicle. Wings in general have a nose-down pitching moment caused by the distribution of lift, both chordwise and spanwise, over typical operating conditions.
One approach for obtaining a wing with an improved airfoil design is set forth in U.S. Pat. No. 4,858,852 to Henne et al. entitled xe2x80x9cDivergent Trailing Edge Airfoilxe2x80x9d, which is incorporated by reference as if fully set forth herein. The methodology set forth in the ""852 patent evaluates the airfoil design in two dimensions (i.e., in a cross-section taken generally perpendicular the longitudinal axis 20 of the wing). Applying the result to the entire span of the wing (i.e., the distance between the centerline of the fuselage of the aircraft and the distal end of the wing) can yield some improvement in the efficiency of wings, but further improvements are possible.
In this regard, we have noted that the application of a xe2x80x9ccontinuousxe2x80x9d divergent trailing edge to a wing may unnecessarily increase the base drag, and the pitching moment of the wing. Accordingly, there remains a need in the art for an improved application of the ""852 patent across the wing trailing edge.
In one preferred form, the present invention provides an improved transonic wing having an inboard wing portion and a mid-span wing portion that is coupled to a distal end of the inboard wing portion. Each of the inboard wing portion and the mid-span wing portion includes a trailing edge base, a high pressure surface connected to the trailing edge base, a low pressure surface opposite the high pressure surface and connected to the trailing edge base and a leading edge connecting the high pressure and low pressure surfaces opposite the trailing edge base. The inboard wing portion is configured such that at least a portion of a trailing portion of the high pressure and low pressure surfaces are defined by slopes forming an included trailing edge angle that converges. The mid-span wing portion is configured such that a trailing portion of the high pressure and low pressure surfaces have slopes that form an included trailing edge angle that diverges. Preferably, the outboard wing portion is configured such that at least a portion of a trailing portion of the high pressure and low pressure surfaces are defined by slopes forming an included trailing edge angle that diverges but to a lesser degree than the mid-span wing.
In another preferred form, the present invention provides a method for forming a transonic wing having a chord and a span. The method includes the steps of: a) providing a baseline transonic wing; b) segregating the baseline transonic airfoil into a plurality of airfoil segments, each of the airfoil segments being defined by a set of characteristics including trailing edge bluntness and trailing edge included angle; c) modifying at least one of the characteristics in the set of characteristics for at least one airfoil segment to provide a modified portion of the wing; and d) tailoring a spanwise variation of the baseline transonic wing to include the plurality of most favorable airfoil segment configurations. Between step (c) and step (d), the methodology may further include the step of assessing an aerodynamic benefit to determine a plurality of most favorable airfoil segment configurations.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.